The present invention relates to coolable airfoils of the type used in high temperature rotary machines such as gas turbine engines.
Efficiency is a primary concern in the design of any gas turbine engine. One principle technique to increase engine efficiency is elevation of core gas path temperatures. Internally cooled components manufactured from high temperature capacity alloys accommodate these elevated temperatures. Turbine stator vanes and blades, for example, are typically cooled using compressor air worked to a higher pressure, but still at a lower temperature than that of the engine core gas path.
Airfoil cooling may be accomplished by, for example, external film cooling, internal air impingement and forced convection either separately or in combination. In forced convection cooling, compressor bleed air flows through internal cavities of the blades and vanes to continuously remove thermal energy. Compressor bleed air enters the cavities through one or more inlets to the internal cavities which then discharge though various exits.
Trailing edge passages direct compressor bleed air around a pedestal array to axially exit through a trailing edge passage of the blade. Recent advances in casting, such as refractory metal core (RMC) technology, facilitates significantly smaller and more complex passages to accommodate the elevated temperatures with a reduced flow of compressor bleed air.
These trailing edge passages may be susceptible to being plugged by dirt and debris such that a minimum passage height must be observed. The passage area determines the cooling flow exit Mach number. As the cooling fluid exits into the engine core gas path, this exit Mach number may be less than optimum from an aerodynamic loss standpoint. To reduce this aerodynamic loss, the passage height restrictions must be circumvented, but to reduce channel heights, the entrances to the trailing edge cooling passage needs to be configured so that dirt and debris cannot enter.